Signature Plastics would be the one to go to in the US, QWERKeys if you're in the UK, Imsto and others if you're in China etc.
Dyesubs use PBT (generally preferred material) for the plastic because it is more porous, and the ink is sublimated (turned from solid into a gas) into the pores of the keycap. The legend permeates the first couple of mm of the key, and doesn't ever wear out essentially. It can produce much more complicated legends than doubleshots can, but you can essentially only make things darker, meaning you can't dyesub light color dyes into dark keys (IE White on Black is impossible) The closer to white the background, the better colors show up. I suggested black on grey because it emulates the game style while being possible, since you're dyeing it a darker color.
Edit: YES I SHOULD! GOOD IDEA! Lol
Btw, I just got 2k 1x WFJ PBTs from SP today. Along with color rings I should have bought ages ago.